Gadolinium-153, with a half-life of 242 days, has been used in the early detection and tracking of osteoporosis. (Osteoporosis is a crippling brittle-bone disease that affects 20 million Americans, mostly women over the age of 45.) Presently it is used as a calibration source for single photon emission computerized tomography (SPECT) cameras. Curie amounts of .sup.153 Gd have been produced in the High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory in Oak Ridge, Tenn; at the Fast Flux Test Facility (FFTF) at the DOE Hanford site in Richland, Wash.; and at the Argonne Test Reactor (ATR) at Idaho Falls, Id., by the nuclear reactions: EQU .sup.151 Eu.sup.(n,.gamma.).fwdarw..sup.152 Eu.sup.(-.beta.).fwdarw..sup.152 Gd.sup.(n,.gamma.).fwdarw..sup.153 Gd.
The isotopic composition of the irradiated Eu target varies with the nuclear reactor properties but is approximately as shown in Table 1.
TABLE 1 Composition of Irradiated Europium (FFTF Reactor) (Basis: 1 g of target RE oxide at discharge) Initial Final Activity Isotope Mass(gm) Mass(gm) (Ci) Half-life, days Eu-150 -- 2.00E - 04 330 5.25E - 01 Eu-151 0.47 2.88E - 01 -- Stable Eu-152 -- 7.66E - 02 13.6 4.82E + 03 Eu-152m -- 1.00E - 04 220 3.88E - 01 Eu-153 0.53 2.34E - 01 -- Stable Eu-154 -- 1.99E - 01 53.8 3.12E + 03 Eu-155 -- 8.70E - 02 40.3 1.81E + 03 Eu-156 -- 7.20E - 03 397.4 1.51E + 01 Sm-150 -- 2.00E - 04 -- Stable Sm-151 -- 1.00E - 06 &lt; 3.18E + 04 Sm-152 -- 1.46E - 02 -- Stable Sm-153 -- 2.00E - 04 86.7 1.96E + 00 Sm-154 -- 1.00E - 04 -- Stable Gd-151 -- 1.00E - 05 0.07 1.20E + 02 Gd-152 -- 6.19E - 02 &lt; 1.10E + 14 Gd-153 -- 1.90E - 03 6.67 2.42E + 2 Gd-154 -- 7.00E - 04 -- Stable Gd-155 -- 2.00E - 03 -- Stable Gd-156 -- 2.05E - 02 -- Stable
All of the samarium isotopes (Table 1) are either stable, generated in insignificant amounts, or have decayed to zero (i.e. Sm-153); and only Eu-152, Eu-154 and Eu-155 contribute to the gamma dose, if the targets are "cooled" for .about.150 days before processing. If the Eu isotopes are 99.999% removed, no additional processing may be required.
Dissolution, separation and purification of Europium from other rare earths including gadolinium has been done as reported by McCoy (1935) and Yost (1946), in which dissolution was in sulfuric acid. Separation began with reducing the Eu.sup.+3 to Eu.sup.+2 with zinc either in the form of zinc dust or as an amalgamated (mercury coated) zinc column in the form of a Jones reductor, followed by precipitating the Eu.sup.+2 fraction as EuSO.sub.4 with the sulfate from the sulfuric acid. Dissolution and separation were in a non-oxidative environment of carbon dioxide (CO.sub.2).
Marsh (1943) reported an improvement over McCoy by using a sodium amalgam. Marsh further recommended against the use of barium sulphate from which the recovery of europium is troublesome even though a barium amalgam resulted in precipitate including europium. He further recommends against the use of zinc dust for rendering bivalent sulfate precipitates unstable.
Ryabchikov (1970) reports that the more soluble rare earths dissolve in weak acids such as acetic, carbonic, and chromic.
More recently, the Oak Ridge National Laboratory has produced .sup.153 Gd by the neutron irradiation of 5 to 10 g of Eu.sub.2 O.sub.3. The resulting europium to gadolinium weight ratio after irradiation in the HFIR approaches 17 (Quinby 1987). To achieve 99.99% radiochemical purity of the .sup.153 Gd product a two step process was used. First, the irradiated europium oxide was dissolved in 1 N sulfuric acid. Second, the solution was placed in an electrochemical cell where 90 to 95% of the energetic (gamma) Eu fraction was removed by electroreduction of Eu(III) to Eu(II) [using zinc electrodes]. Argon was used as a cover gas. High pressure ion exchange was then used to remove additional Eu(III) and sulfuric acid to obtain a gadolinium product of 99.9% purity. This process has the disadvantages of low production (7 g batches of Eu oxide), poor yields (.about.70%) of .sup.153 Gd, and the need for the high pressure ion exchange.
Also Wheelwright (1986) described a method to separate Eu on a large scale (.about.60 grams) from the Gd-Sm fraction prior to final purification. During the `First Cycle of Chemical Purification` Eu.sub.2 O.sub.3 targets were dissolved. When dissolution was complete, the Eu(III) was reduced to Eu(II). Further chemical purification by ion exchange was then required to separate the Gd from a trace of Eu and the Sm. This was accomplished by ion exchange band displacement (Wheelwright; 1969, 1973).
After separation of the major fraction of the Eu isotopes, to prevent irradiation damage to the organic ion exchange resin, Campbell (1973) and Elbanowski (1985) suggested the use of high-pressure ion exchange for final purification.
A solvent extraction process in which the Gd was extracted away from the Eu by use of di(2-ethylhexyl)phosphoric acid after the reduction of Eu to the divalent form was also investigated by Posey (1986).
However, there still remains a need in the art of gadolinium separation for a method having a higher production and yield.